Photosynthesis
Fotosyntes
BiologyRare
Discovered 1779 · Jan Ingenhousz
SPARKON10 / 10
Photosynthesis
The ideaPlants use light to build sugar from carbon dioxide and water, and give off oxygen.
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Lets you predictMost of a tree's mass comes from the air.
Tests usually ask
  • The balanced formula
  • Where the energy comes from
Scan for the full explanation and a practice question.
SPARKON · 10 / 10
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Biology ◆ Rare: a famous discovery

Photosynthesis

Swedish: Fotosyntes · Discovered: Jan Ingenhousz showed light is needed, 1779

Plants use light to build sugar from carbon dioxide and water, and give off oxygen.

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Why it works

A tree does not get heavy by eating soil. The carbon in the wood comes from carbon dioxide in the air; light energy is stored in the sugar.

The oxygen you breathe was released by plants and algae. Burning wood or food runs photosynthesis backwards and gets the energy out again.

What it lets you predict

Most of a tree's mass comes from the air.

How tests ask about it

  • The balanced formula
  • Where the energy comes from

Try it

A small tree gains 50 kg over ten years, but the soil in its pot is almost unchanged. Where did the mass come from?

Show the answer

Mostly from carbon dioxide in the air, plus water.

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